Arduino Forum

(This post is based partly on suggestions by @hiduino, @Graynomad, and @CrossRoads seen here: http://arduino.cc/forum/index.php/topic,128582.msg972824.html#msg972824http://arduino.cc/forum/index.php/topic,128582.msg967376.html#msg967376http://arduino.cc/forum/index.php/topic,136243.msg1026496.html#msg1026496)

Since there are numerous existent Arduino shields with 5V signal levels, versus the 3.3V level at which the Arduino Due runs, users would need to have some solution to maintain interfacing compatibility.

This in-between shield would be inserted first into the Due, and on top of the shield would be inserted any arbitrary existent Arduino shield.

To allow separation for routing between the 5V shield lines and the 3.3V Due lines via the level translators, the in-between shield could have either slightly offset headers&sockets, or else surface mount headers on the bottom.

In contrast to resistor/diode-based methods, the above level-translator IC based solution should work bi-directionally, for all signal types (digital I/O, PWM, analog lines, Serial, SPI, I2C), and thus for all shields.

Any thoughts or issues seen regarding this Adapter-Shield approach?

Perhaps someone (or the Arduino dev team) can design a shield like the above.

@CrossRoads:Looking good -- That layout image of yours is just to show the orientation and not the actual level translation itself, yes? Have you looked into the GTL2000... or the TXB0108 would work too, although I believe the GTL2000 is significantly cheaper.

Yes, it was just to get the headers defined, to show that 2 sets of headers could be made to fit next to each other - males down to the Due, and females up to shields.I think I'll slide the 2nd set over some more to make room for signals to be buffered in the middle area and then go back out, especially in the double row area.Are there many mega shields? Maybe just drop that area and make sure the 20 Uno IO + power + ICSP headers are supported. Need to beef up the power traces.

Crossroads (with the system calling me "derekmjenkins" for some reason - hopefully just a test towards solving my week day log in problems)

I was thinking just TXB0108s or maybe a couple of GTL2000 for the bank of 18 header pins.Bring the analog straight over, with TXB0108 in parallel, maybe a jumper to enable the OE/ when digital was required.Or couple TXB0104s so analog/digital could be split up some.

Really stinks not being able to log in during the day except occasionally due to system conflicts or something.

A crosspoint switch would be one way to go, you'd need a lot for them and last I looked they were not cheap. Also I don't think they level shift but at least they should pass the analog.

As for the analog you can get programmable gain chips or just make your own with opamps.

Either way you need more IO to control this lot, so add 1 or 2 I2C IO expander chips with jumpers to set the address so they don't clash with any shields.

In general I like the basic concept but it could very quickly turn into a cluster f*ck with 30 chips that cost 2x the Due and the shield you want to use.

Crossroads (aka derekmjenkins!?), you've obviously made a start, any thoughts on doing something?

Quote

Are there many mega shields?

I don't think so, I'd drop the extra stuff and just go for a standard shield.

EDIT: I just looked at the price for that CD22M3494 crosspoint switch, it's not too bad but still too much for this I think.

______Rob

Hey Rob, got a solution for ya.

http://www.ti.com/product/sn74lvc16t245 (http://www.ti.com/product/sn74lvc16t245) (I think there is a 32 channel unit as well)

Use something like this after a crosspoint switch and before exiting the shield. That way, each pin's output voltage can be selected and each pin can by dynamically assigned. Also, why do you think this would be too expensive? Mouser has the level shifter I just mentioned at $2 and the crosspoint at $4 or 6. Plus other parts and custom fab, you could almost surely get away under $20.

EDIT: Just thinking, you would just need the crosspoint for the pins that need to be moved like SCL and SDA, then just use a couple more of the level shifters I mentioned for the rest of the I/O. That way, the pins that might need to be moved can be, while all the pins can still be selected to be either 5v or 3.3v.

Here is what I'm thinking. This first drawing is a rough schematic for just the crosspoint section of pins. Other pins could be added to these and all the rest of the pins would need to be passed through 74LVC16245's as well.

(http://dl.dropbox.com/u/55783756/Photos/possible%20diagram.png)

Red trace is on bottom

Blue is on top

Black is on bottom (5v, 3.3v, gnd)

To answer you question about the pins, Mayhew Labs came up with a pretty nice solution.

Here's the schematic & layout, please create a version with the parts you are suggesting.Top & bottom mount surface mount headers would be one way to keep the physical board the same size, as long as its cut back from the USB header.

Ok so here's the diagram of the circuit as I see it. Let me know what you guys think

Circuit for pins who's position might need to be changed

(http://dl.dropbox.com/u/55783756/Photos/crosspointIncluded.png)

And here is for the other pins who's position is fixed

(http://dl.dropbox.com/u/55783756/Photos/NoCrosspointIncluded.png)

For both the CD22M3494 (crosspoint) and the SN74LVC16T245 (logic shifter) I think the buses can be 16 bit wide. As for going with the SN74LVC16T245 over the TXB0108, the advantage I see is that with the SN74LVC16T245, you can select each pin's output so some pins could interface with 5v logic, while others with devices at 3.3v. Might as well keep the shield dynamic as we can, especially if things really are moving towards 3.3v logic. Just my two cents, what's your guys reaction?

Here's the schematic & layout, please create a version with the parts you are suggesting.Top & bottom mount surface mount headers would be one way to keep the physical board the same size, as long as its cut back from the USB header.

I tried the TXB0108 and finally gave up. The blue boxes in the attached picture contain 3 pcs pf TXB0108.I made the beta board and tested it. While I test the TXB0108 5V output with voltmeter, the voltage is 3V. However, I test it with oscilloscope, the output is 5V. I touch the wire or chip with my finger, the voltage became unstable. Well, I think, the TXB0108 is easy to go into self-excited oscillation process. And the load capacity is small. If I connect other devices to it through long cables, such as a digital sensor, the output may have problem. However, if I intert the sensor in the header of the beta DUE board directly, it works fine.I tried many time but still didn't success. Not sure if the TXB0108 performs not good enough.

With the setup, each pin can be selected as 3.3v or 5v through the MUX, then routed through the logic shifter if it is 5v. After that, the crosspoint handles the pin reassignment if needed. How about this? We getting close?

Maybe there is a market after all, I always was 180 degrees out of phase with the consumer :)

Dan, my last question? How does the logic shifting circuit have bi-directional IO?_____Rob

I would say if there is a market for the Due - then there is a market for this shield. To choose the Due over the raspberry pi the main feature is the general purpose IO and the existing shields. But to use either of these such a board is extremely useful.

Not only would a significant percentage of Due purchasers want such a shield- there would also be a market of people who current do NOT choose a Due to to shield incompatibility!

Hello, read through those comments and is amaze with it. But i still got doubt. Please help me. Im so wan the 12 bit PWM provided by the I/O pins from this arduino due. But my concern are: 1. whether those logic level converter IC can work this 12 bits PWM? because im doing with hall sensor geared motor, worry that the accuracy will be affected.2. is those bi-directional converter? means if i attach all the digital pins to the converter, can i read/write data as other arduino board? 3. can those work with analog pins?

I find this shield very usable. I would like to use it as interface for drivers of stepper drivers. These drivers require 5V, and arduino due can output only 3.3V.

So where is this "way to do this with very good compatibility for all/most shields"?Schematic? Pcb ?

Can this shield be bought somewhere already? It's old post...

OK I found this guy: https://digistump.com/wiki/digix/tutorials/levelshifter (https://digistump.com/wiki/digix/tutorials/levelshifter)

http://digistump.com/products/51 (http://digistump.com/products/51)I see it costs 14$ in USA, but i'm from Europe, can somebody suggest me similar shield and to be able to buy it here in old continent :) ?